Many drugs and environmental compounds are low molecular weight molecules that can couple to proteins and function as haptens, evoking deleterious T lymphocyte responses. Current treatments are generally directed to amelioration of symptoms. However, advances in understanding the mechanism of T-cell antigen recognition suggests that therapies directed to specific T cells may be possible. The long-term objective of the proposed research is to develop an immunotherapeutic approach to anergize or otherwise deviate hapten-specific effector T cells. The approach is to define simple compounds that are recognized by hapten-specific T cells in the context of class II Major Histocompatibility Complex (MHC) molecules, and later to use such compounds to test desensitization of individuals sensitive to specific haptens.